摘要:

A two‐chamber‐system was used to study whole‐plant gas exchange responses ofSpartina alterniflorato long‐term and transient salinity treatments over the range of 5 to 40 ppt NaCl. Lower photosynthetic rates, leaf water vapor conductances, belowground respiration rates, and higher aboveground respiration rates in plants adapted to 40 ppt NaCl were observed. Area‐specific leaf weight increased with salinity, although the salt content of leaf tissues did not. A reduced rate of gross photosynthesis and higher aboveground respiration rate in 40‐ppt NaCl plants significantly lowered the net whole‐plant CO2gain below that of 5‐ppt NaCl plants, while the net CO2gain of 25‐ppt NaCl plants was intermediate. Within 6 hr of increasing the salinity of 5‐ and 25‐ppt NaCl plants by 20 and 15 ppt NaCl,S. alternifloraresponded by reducing leaf water vapor conductance, which in turn reduced the photosynthetic rate. This response was reversed by returning the plants to their original salinity, which indicates thatS. alternifloraadjusts water loss and gas exchange in response to transient salinity stress by regulating stomatal aperture. On the other hand, decreasing salinity of the growth media of plants cultured at 25 and 40 ppt NaCl had little or no effect on gas exchange characteristics. This suggests thatS. alternifloraadapts to constant salinity through fixed, salinity‐dependent structural modifications, such as stomatal density.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1994.tb15500.x

出版商:Wiley    

年代:1994

数据来源: WILEY

摘要:

In this paper we describe the first anatomically preserved Mesozoic seed fern cupule–Petriellaea.The multiovulate cupules were produced singly at the end of a short dichotomizing axis. Cupules are bilateral with a dorsal groove and transverse narrow ventral opening. The vascular system of the cupule consists of a series of traces that extend up the dorsal surface of the cupule and down the ventral face. Ovules are orthotropus, sessile, and borne on the adaxial surface of the leaflike cupule either singly or in multiple rows. They are up to 1.5 mm long, triangular in transverse section, and characterized by a multilayered integument. Nucellus and integument are fused throughout their length, but no pollen chamber is present. In the chalaza is a small vascular disc of transfusion tracheids that represents the extent of the ovule vascular system. Ovules are interpreted as being fossilized at a prepollination stage, although a few possess some evidence of a cellularized megagametophyte. These permineralized cupules indicate that in at least one Mesozoic seed fern group, ovule enclosure resulted from the transverse folding (tip to petiole) of a megasporophyll bearing adaxial ovules. Cupule morphology and ovule enclosure in other Late Paleozoic and Mesozoic seed ferns is discussed.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1994.tb15501.x

出版商:Wiley    

年代:1994

数据来源: WILEY

摘要:

The present paper details the anatomy of permineralized foliar specimens ofGigantonoclea guizhouensisGu and Zhi (Gigantopteridales) from the Upper Permian of western Guizhou Province in southwest China. In addition to reticulate venation, these fossil leaves possess a number of interesting anatomical features including: multicellular spines on the midrib, hypodermal sclerenchyma ribs, U‐ or V‐shaped xylem in the midrib and secondary veins, tracheids with various secondary wall thickening patterns, paracytic stomata on the abaxial surface, epidermal cells with sinuous anticlinal walls, and secretory cavities in the mesophyll. Based on anatomical features, a liane habit is suggested, and the systematic differences amongGigantonoclea guizhouensis, Gigantopteridium, and the North American taxonDelnorteaare underscored.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1994.tb15502.x

出版商:Wiley    

年代:1994

数据来源: WILEY

摘要:

In this paper we describe a fossil fungus–Paleoblastocladia millerigen. et sp. nov.–from the 400 million‐year‐old Early Devonian Rhynie chert that shares numerous features with modern zoosporic fungi placed in the order Blastocladiales. The fungus occurs in tufts that arise from stomata or between the cuticle and epidermis ofAglaophyton majoraxes. Thallus development begins from an irregular bipolar basal cell that produces a system of intramatrical rhizoids and clavate‐shaped extramatrical, nonseptate hyphae. These hyphae develop into two types of mature thalli. Sporothalli are characterized by several orders of dichotomous branching and the production of terminal, globose zoosporangia, as well as thick‐walled, pitted resting sporangia. On separate dichotomously branched thalli (gametothalli) are terminal chains of two or three gametangia, in which the terminal one is slightly larger. Despite the fact that all of the reproductive organs contain either zoospores or gametes, none show evidence of discharge papillae. The fossil fungus is compared with extant members of the Blastocladiales, and the presence of sexual reproduction is discussed.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1994.tb15503.x

出版商:Wiley    

年代:1994

数据来源: WILEY

摘要:

Well‐preserved petrified woods from the Maastrichtian of Big Bend National Park, Texas, with a combination of characters seen in the Malvales are described asJavelinoxylon multiporosumgen. et sp. nov. One log is over 70 cm in diameter and is riddled with termite galleries; this specimen provides additional documentation for the occurrence of dicotyledonous trees in the Late Cretaceous. These woods have structure different from any other known Cretaceous dicotyledonous wood and are advanced in the Baileyan sense as vessel elements are relatively short, perforations are exclusively simple, vessels are commonly in long radial multiples, and rays are storied. This is the earliest record for woods with storied structure. The occurrence of large dicotyledonous trees with advanced wood structure in Big Bend suggests there were differences between the Late Cretaceous vegetation of the northern Rocky Mountains and the Big Bend region.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1994.tb15504.x

出版商:Wiley    

年代:1994

数据来源: WILEY

摘要:

Increasing photosynthetic photon flux density (PPFD) received during development from 5.5 to 31.2 mol m‐2d‐1resulted in greater leaf and mesophyll cell surface areas in cotton (Gossypium hirsutumL.). The relationships between the amounts of these surface areas and potential CO2assimilation by these leaves were evaluated. Leaf area (epidermal surface area of one side of a leaf), mesophyll cell surface area, and net rate of CO2uptake (Pn) were measured from the time leaves first unfolded until P., was substantially reduced. At the higher PPFD, leaf and mesophyll surface areas increased more rapidly during expansion, and Pnper unit leaf area was greater than at the lower PPFD. Although leaves at the higher PPFD reached the maximum P., per unit mesophyll cell surface area 4 to 5 days earlier than leaves at the lower PPFD, the maxima for these P., were similar. Leaves grown at the higher PPFD had the potential to assimilate 2.2, 3.5, or 5.8 times the amount of CO2as leaves from the lower PPFD when P., was expressed per unit mesophyll surface, per unit leaf surface, or per whole leaf, respectively. Greater and earlier development of both P., and mesophyll cell surface area at higher PPFD apparently had a compounding effect on the potential for carbon assimilation by a leaf.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1994.tb15505.x

出版商:Wiley    

年代:1994

数据来源: WILEY

摘要:

Monotropsis odorataElliott. is one of the most cryptic and relatively rare North American endemic species of the Monotropaceae; therefore, information concerning the biology of this achlorophyllous, mycotrophic angiosperm is limited. Bright field and fluorescence microscopic investigations of postpollination gynoecia reveal that pollen tubes follow a continuous pathway from the receptive surface of the stigma to micropyles of the ovules. The pollen tube pathway is characterized by discrete strands of transmitting tissue connecting an exudate‐coated stigma to an exudate‐filled, stylar canal that leads directly to exudate‐coated placentae. Pollen tube growth appears restricted to those areas associated with an exudate. The gynoecial pathway for pollen tube growth in this taxon conforms to those described from other monotropàceous species.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1994.tb15506.x

出版商:Wiley    

年代:1994

数据来源: WILEY

摘要:

We studied the leaf structural, water status, and fast fluorescence responses of two palms,Socratea exorrhizaandScheelea zonensis, under natural dry season conditions in a clearing (high light [HL] palms) and the forest understory (low light [LL]palms) on Barro Colorado Island, Panama. HL‐Socratealeaves were more shade‐adapted, less xeromorphic, and more strongly affected by drought than HL‐Scheelea.Fv/Fm(the ratio of variable to maximum chlorophyll fluorescence) and t½(the half‐rise time of Fm) was lower in HL‐leaves of both species, indicating photoinhibition. In HL‐Scheelea, the light‐induced reduction of Fv/Fmwas much less than in HL‐Socratea, and Fv/Fmrecovered completely overnight. Patterns of relative water content, specific leaf dry weight, stable carbon isotope composition, and leaf conductance suggest that increased drought resistance inScheeleareduces susceptibility to photoinhibition. An increase in Foindicated the inactivation of PSII reaction centers in HL‐Socratea.The very low chlorophyll a/b ratio and alterations in chloroplast ultrastructure in HL‐Socrateaare consistent with photoinhibition. Under LL, the species showed no appreciable interspecific differences in chlorophyll fluorescence. Excess light leads to low values of Fv/Fmin HL‐plants relative to LL‐plants on both leaf surfaces, particularly on the lower surface, due to a decrease of Fmin both surfaces and an increase in F., of lower surface. For both species, Fofor the lower surfaces of HL‐plants was higher and t½was markedly lower than for the upper surface, as is typical for shade‐adapted leaves. Xeromorphic leaf structure may reduce susceptibility to photoinhibition during the dry season. Drought‐enhanced photoinhibition could limit the ability of some species to exploit treefall gaps.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1994.tb15507.x

出版商:Wiley    

年代:1994

数据来源: WILEY

摘要:

This study was conducted using scanning electron microscopy to characterize morphological changes in the maturing perennial ryegrass (Lolium perenneL.) coleorhiza and emerging radicle during continuous hydration or hydration interrupted by dehydration. With continuous hydration, coleorhizae emerged and cell expansion led to a progressive increase in tissue size. Coleorhiza cells developed extensions like epidermal root hairs. Although coleorhiza cells appeared undamaged by radicle emergence, they began deteriorating when the radicle had reached a length of approximately 2 mm. In response to dehydration, coleorhiza cells shrank but did not rupture. If dehydration was initiated during an early stage of coleorhiza development, greater tissue shrinkage occurred at ‐150 MPa than at ‐4 MPa; otherwise, coleorhizae showed no differential response due to dehydration water potential. Upon rehydration, coleorhizae dehydrated at ‐4 MPa regained cell turgor within 24 hr, while coleorhizae dehydrated at ‐150 MPa did not. Loss of the coleorhiza (due to desiccation) did not preclude radicle emergence, which occurred upon rehydration. Radicles up to 2 mm in length were more tolerant of dehydration than were coleorhizae. These results suggest that the coleorhiza may be an expendable tissue during germination, as its likely protective and absorptive roles are lost following a single harsh dehydration event.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1994.tb15508.x

出版商:Wiley    

年代:1994

数据来源: WILEY

摘要:

The patterns of initiation and early development of the minor and major veins in the flat portion of the leaf blade of maize (Zea maysL.) follow similar patterns. The veins and their associated bundle sheath cells commonly arise from cell assemblages derived from a single cell lineage, or longitudinal file of cells, rather than from two “half vein units” derived from different cell lineages. In addition, apparently, none of the vascular cells derived from the procambium is directly related ontogenetically to a bundle sheath cell. In veins derived from larger cell assemblages, the lateral bundle sheath cells are more closely related ontogenetically to the mesophyll cells, which are derived from the ground meristem, than to the vascular cells, which are derived from procambium. The bundle sheath cells, accordingly, are interpreted as being ground meristem in origin.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1994.tb15509.x

出版商:Wiley    

年代:1994

数据来源: WILEY